Multicolor striped or mosaic form optical filters are used for color image pick-up tubes or color solid state image pick-up devices, such as color metal oxide semiconductor (MOS) devices, charged coupled devices (CCD), and charged injection devices (CID). A multicolor optical filter is usually composed of the three colors of red, green, and blue (additive process), or three colors of cyan, magenta, and yellow (subtractive process), regularly arranged in a stripe or mosaic form. Of course, the color composition of such multicolor optical filters is not necessarily limited to the three color systems. Provided that red, green, and blue output signals are finally obtained, the multicolor optical filter may be composed of two colors. For instance, it may be composed of white light and two colors of the foregoing additive or subtractive process three colors. As described hereinafter, these three signals can be easily converted into red, green, and blue output signals by an arithmetic circuit.
Conventional multicolor optical filters include a filter prepared using dichromic mirrors, as described, for example, in Japanese Patent Publication No. 8590/65 and Japanese Patent Application (OPI) No. 3440/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and a filter prepared by dyeing a polymeric material layer with dyes as described, for example, in Japanese Patent Application (OPI) Nos. 37237/72, 63739/73, and 66853/73, and Japanese Patent Publication No. 248/78.
Processes for the production of such conventional multicolor optical filters, however, are very complicated and troublesome, because a procedure comprising the steps of coating a photoresist, imagewise exposure of the photoresist (which in turn involves precise alignment of a mask on the photoresist layer), development of the exposed layer, coloring or decoloring, and removing the resist, is required for the formation of a pattern for each color in the system, and the procedure must be repeated several times (usually three or more times).
In practice, these processes require additional steps to obtain excellent multicolor optical filters. For example, in the case of producing multicolor optical filters by repeating several times the steps of coating a photoresist such as gelatin dichromate, imagewise exposure, formation of a relief pattern by development, and coloring, it is necessary to prevent a colored pattern formed in a previous coloring step from mixing with a different color in a subsequent color step. For this purpose, it is necessary to provide a protective layer, which will not be dyed, on the surface of a pattern-bearing layer in between the coloring steps, as described in Japanese Patent Application (OPI) No. 37237/72. This gives rise to the problems that the process becomes complicated and the multicolor optical filter obtained is very expensive.
In order to solve the foregoing problems, a process utilizing silver salt color photographic materials (hereinafter referred to as "color films") has been proposed. In accordance with the proposed process, a coupler-in-emulsion type or coupler-in-developer type color film is exposed to light through red, green, and blue master filters, or cyan, magenta, and yellow master filters, and is then subjected to ordinary color development to form a color filter composed of cyan, magenta, and yellow colors, or red, green, and blue colors, respectively, and the color film so formed is adhered to a glass disc such as a face plate of an image pick-up tube, and a thin glass plate is adhered to the color filter, to provide the desired multicolor optical filter.
In the color film used in the foregoing process, however, the size of silver halide grains in the emulsions is significantly large, and the emulsion layers are present in a multilayer structure wherein each emulsion layer has a sensitivity in its specific spectral wavelength region. Consequently, the scattering of light in the emulsion layers is severe, and therefore the resolving power of the color film is not so high.
U.S. Pat. No. 4,271,246 discloses a technique to obtain a very high resolving power by the use of a combination of a photographic light-sensitive material having known black-and-white fine grain silver halide emulsions and a coupler-in-developer type color development. This technique, however, requires at least three light-exposure and color development steps, and hence is very complicated.
Furthermore, in accordance with the conventional processes, it is necessary to use a specific mask in which red, green, and blue filters are arranged in a mosaic form for the light-exposure, and complicated steps are required to make the mask precise.